Such a combustion chamber assembly unit is known from DE 10 2013 220 654 A1. This combustion chamber assembly unit comprises a combustion chamber housing with an essentially cylindrical circumferential wall extending in the direction of a combustion chamber housing longitudinal axis and with a bottom area fixed at an axial end area of the circumferential wall. The circumferential wall and the bottom area define a combustion chamber, into which fuel is admitted via a porous evaporating medium carried on an evaporating medium carrier of the bottom area. The combustion air needed for combustion is fed via an air admission opening arrangement, which comprises a plurality of air admission openings arranged distributed in the axial direction and in the circumferential direction in an axial area of the circumferential wall between the porous evaporating medium and a flame diaphragm carried on the circumferential wall. An electrically energizable heating device is provided at the bottom area for supporting the fuel evaporation from the porous evaporating medium especially in a start phase of the combustion operation. The electrically energizable heating device is positioned on a side of the evaporating medium carrier facing away from the porous evaporating medium and thus also away from the combustion chamber. An electrically energizable ignition element extending into the combustion chamber at a short distance to the surface of the porous evaporating medium facing the combustion chamber and essentially parallel to this surface is carried on the circumferential wall.